This is a small grant proposal to test new methods of psychiatric/behavioral treatment. Previous research by Edmond Dewan and by this UCSD group has suggested that night light can shorten and regularize the menstrual cycles of women with long and irregular menstrual cycles. Some menstrual irregularities may arise from behavioral aberrations in how women expose themselves to bright and dim illumination. Further testing of new night light methods and techniques is necessary to further validate the treatment methods and timing (in terms of both time-of-the-month and time-of-night), to extend dose/response testing, and to further assess the comfort and reliability of lighted sleep masks. Sixty paid female volunteers with menstrual cycles of 35-60 days will be recruited. Each subject will be followed prospectively for a baseline menstrual cycle, and then will be randomized to night light treatment on nights 13-17 after the onset of menstruation. Treatments assigned by stratified randomization will consist of 250 flux white light (a treatment previously demonstrated to be effective), 25 lux, 2.5 lux, or 0.025 lux (a placebo). In the following two menstrual cycles, conditional crossover treatments will be added. If the subject responds to the first treatment, it will be repeated in the second and third treatment cycles. If the subject fails to respond in the first or second cycles, the treatment intensity will be stepped-up. If a reliable methodology of regulating menstrual cycles with night lights can be demonstrated, this approach might lead to valuable methods of assisting behavioral (rhythm) contraception and to new approaches to infertility.